The present invention relates to a high critical temperature superconducting Josephson device formed on a bicrystal substrate, and to a method for manufacturing it.
Conventional high critical temperature superconducting Josephson devices formed on bicrystal substrates are described, for example, in "Orientation Dependence of Grain-Boundary Critical Currents in YBa.sub.2 Cu.sub.3 O.sub.7-.delta. Bicrystals", D. Dimos et al., Physical Review Letters, Vol. 61, Number 2, 1988, pp. 219-222, and "Superconducting Transport Properties of Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+x Bicrystal Grain Boundary Junctions", B. Mayer et al., Appl. Phys. Lett., Vol. 63 (7), 16 Aug. 1993, pp. 996-998.
These references describe that a Josephson Junction, wherein a superconducting bridge encloses a barrier part with weak superconducting properties (i.e., insulating part) is formed by epitaxially growing a superconducting thin film on a bicrystal line which is a Junction surface of a bicrystal substrate so that the crystal grain-boundaries are collected together exactly on the bicrystal line.
However, in the conventional Josephson device, the properties of the barrier part have a dependence on various conditions such as the linearity of the bicrystal line and the method of growing the superconducting oxide film, hence production yields of the Josephson device were poor. Further, as it is difficult to control the properties of fine crystal grain boundaries having a size of nanometer levels or below, it was technically difficult to provide a high critical temperature superconducting Josephson allay having an uniform critical current.